feat: display enterprise account credit and spend usage rows

For users on an enterprise Claude plan (no five-hour / seven-day rate-limit
buckets), the widget now shows two dedicated rows:

  Cr  9%·20/6   — credit remaining (%) and expiry date in system locale format
  Sp  $12/$50   — spend used / spend limit

For personal (Pro/Free) accounts the rows continue to show the normal 5h/7d
rate-limit bars.

Implementation notes:
- Parses `cinder_cove` and `spend` fields from the usage endpoint response
- Locale-aware date format via GetLocaleInfoW (respects separator and D/M order)
- Disk cache at %APPDATA%\ClaudeCodeUsageMonitor\account_cache.json survives
  widget restarts; cleared when plan has no enterprise fields (prevents stale
  enterprise rows appearing for Pro users after a 429)
- Tray tooltip uses dynamic row labels ("Cr"/"Sp" vs "5h"/"7d")
- tray_icon.rs: guard empty text before DrawTextW to avoid GDI crash

Author: oyardena

src/models.rs

@@ -4,6 +4,7 @@ use std::time::SystemTime;
 pub struct UsageSection {
     pub percentage: f64,
     pub resets_at: Option<SystemTime>,
+    pub has_bucket: bool,
 }
 
 #[derive(Clone, Debug, Default)]
@@ -12,9 +13,18 @@ pub struct UsageData {
     pub weekly: UsageSection,
 }
 
+#[derive(Clone, Debug, Default)]
+pub struct AccountUsage {
+    pub credit_pct: f64,
+    pub credit_expiry: Option<SystemTime>,
+    pub spend_used: f64,
+    pub spend_limit: f64,
+}
+
 #[derive(Clone, Debug, Default)]
 pub struct AppUsageData {
     pub claude_code: Option<UsageData>,
     pub codex: Option<UsageData>,
     pub antigravity: Option<UsageData>,
+    pub account: Option<AccountUsage>,
 }

src/native_interop.rs

@@ -1,9 +1,14 @@
 use windows::core::PCWSTR;
 use windows::Win32::Foundation::{BOOL, HWND, LPARAM, RECT};
+use windows::Win32::Globalization::GetLocaleInfoW;
 use windows::Win32::UI::Accessibility::{SetWinEventHook, UnhookWinEvent, HWINEVENTHOOK};
 use windows::Win32::UI::Shell::{SHAppBarMessage, ABM_GETTASKBARPOS, APPBARDATA};
 use windows::Win32::UI::WindowsAndMessaging::*;
 
+const LOCALE_USER_DEFAULT: u32 = 0x0400;
+// Short date format pattern (e.g. "M/d/yyyy")
+const LOCALE_SSHORTDATE: u32 = 0x001F;
+
 // Window style constants
 pub const WS_POPUP_STYLE: u32 = 0x80000000;
 pub const WS_CHILD_STYLE: u32 = 0x40000000;
@@ -181,6 +186,41 @@ pub fn wide_str(s: &str) -> Vec<u16> {
     s.encode_utf16().chain(std::iter::once(0)).collect()
 }
 
+/// Format a month/day pair respecting the Windows system locale
+/// (separator, and whether day or month comes first).
+/// Returns e.g. "9/15" (en-US), "15/9" (en-GB), "15.9" (de-DE).
+pub fn format_month_day_locale(month: u8, day: u8) -> String {
+    if let Some(pattern) = locale_short_date_pattern() {
+        let lower = pattern.to_lowercase();
+        // Find the separator: first non-alphabetic, non-quote character
+        let sep = lower
+            .chars()
+            .find(|c| !c.is_alphabetic() && *c != '\'')
+            .unwrap_or('/');
+        // day-first when 'd' appears before 'm' in the pattern (e.g. "dd/MM/yyyy")
+        let d_pos = lower.find('d');
+        let m_pos = lower.find('m');
+        return match (d_pos, m_pos) {
+            (Some(d), Some(m)) if d < m => format!("{}{}{}", day, sep, month),
+            (Some(_), Some(_)) => format!("{}{}{}", month, sep, day),
+            _ => format!("{}/{}", month, day), // malformed pattern — safe fallback
+        };
+    }
+    format!("{}/{}", month, day)
+}
+
+fn locale_short_date_pattern() -> Option<String> {
+    unsafe {
+        let mut buf = [0u16; 256];
+        let len = GetLocaleInfoW(LOCALE_USER_DEFAULT, LOCALE_SSHORTDATE, Some(&mut buf));
+        if len > 1 && (len as usize) <= buf.len() {
+            Some(String::from_utf16_lossy(&buf[..len as usize - 1]).to_string())
+        } else {
+            None
+        }
+    }
+}
+
 /// COLORREF wrapper (RGB packed into u32)
 pub fn colorref(r: u8, g: u8, b: u8) -> u32 {
     r as u32 | (g as u32) << 8 | (b as u32) << 16